Capturing Unstable Carbanionic Intermediates via Halogen Transfer: Base-Promoted Oxidative Coupling Reactions of...

We describe how the merger of deprotonation, halogenation, and substitution into compatible processes enables the productive functionalization of traditionally unstable carbanionic intermediates. This strategy enables the first oxidative coupling protocol of α,α-difluorobenzylic C─H bonds with heteronucleophiles. Here, transiently generated α,α-difluorobenzylic carbanionic intermediates undergo halogen transfer from 2-bromothiophenes to form electrophilic ArCF₂Br compounds for in situ nucleophilic substitution, thereby avoiding α-fluoride elimination pathways that typically plague α-fluorocarbanions. This method streamlines the modular synthesis of α,α-difluorobenzyl(thio)ethers and led to the broader realization that halogen transfer to unstable carbanions is an enabling principle across diverse C(sp²)─H and C(sp³)─H systems.